This invention relates to an element monitoring apparatus and particularly to such apparatus for continuously monitoring the interconnection of a lid opening key on a can lid.
In cans for beverages and the like, the one end or lid is provided with an opening tab or key which when pivoted outwardly and pulled removes a scored portion of the lid to form a discharge opening. Automated lid forming apparatus has been developed in which the can lid is automatically fed through a series of shaping and forming stations including a key attaching station at which a key is attached. The formed lids are assembled and subsequently applied in a rapid and automated movement to close the filled cans. In such systems, a key monitoring means is provided in the forming apparatus or immediately therefrom to detect missing keys and to reject any lid or end in which the key is missing. If a key is not detected, the forming apparatus preferably stops and permits the operator to check on the type of malfunction. Various key detection systems have been employed.
In one existing key detection system, a spring loaded plunger is located in the forming tool immediately downstream of the station and includes an external arm protruding into alignment with a limit microswitch. The detector switch is normally closed with the key properly in position. If a key is not staked in place, the switch mechanically opens, energizing the appropriate control to terminate press operation and/or providing a signal to an ejection station to eject the appropriate keyless end or lid from the assembly line. In place of the microswitch, a proximity switch can, of course, be provided coupled to the follower arm movement. Other systems have employed monitoring of the presence or lack of a key by use of a proximity switch at a checking station through which each finished lid is moved through the downstream portion of the forming apparatus. In one system, a finished lid is placed in an appropriate belt port and moved past a sensing head. Although such systems are widely employed, the mechanical readjustment of the mechanical force transmission require relatively accurate adjustment which as a result of the high speed operations and the like can readily come out of adjustment with use. In the downstream protection systems, the various monitoring and memory means must be provided to provide the appropriate control and of course require additional machine stations. Further, such systems may not provide a fail-safe operation. Thus if the detection system fails, defective keyless lids can be rapidly produced and fed through the line for the automatic application to the beverage cans. Such cans, of course, cannot be marketed under normal marketing procedures and constitute loss production.
There is a need to provide a more reliable automated key detection means for detecting of the presence of a key and preferably within the downstream forming station.